1. Field of the Invention
The present invention relates to a method and system for transmitting/receiving messages in a wireless communication system, and more particularly to a method and system for transmitting/receiving neighbor base-station advertisement messages broadcast by a base station in a broadband wireless access (BWA) system.
2. Description of the Related Art
Fourth generation (4G) communication systems, which are the next generation communication systems, are being designed to provide users with services having various Qualities of Service (QoS) and supporting a transmission speed of about 100 Mbps. Particularly, in current 4G communication systems, research is being undertaken to support a high-speed service by ensuring mobility and QoS in broadband wireless access communication systems, such as a local area network (LAN) system and a metropolitan area network (MAN) system. A representative communication system currently being developed is known as an IEEE (Institute of Electrical and Electronics Engineers) 802.16 communication system.
Compared with conventional wireless technologies for providing voice services, the IEEE 802.16 communication system enables the transmission of data in a shorter period of time than needed if using conventional communication technologies, by providing a wider data bandwidth, and can efficiently use channels by sharing all user channels. In addition, the IEEE 802.16 communication system ensures QoS, so that users can receive services of different QoS depending on the characteristics of the services.
From among the IEEE 802.16 communication system, an IEEE 802.16a communication system does not take into consideration the mobility of a terminal, while an IEEE 802.16e communication system takes into consideration the mobility of a terminal (e.g., a mobile station).
Therefore, in the IEEE 802.16e communication system, a base station periodically broadcasts a MOB_NBR-ADV (mobile neighbor advertisement) message, which is information about neighbor base stations, to all mobile stations located in a corresponding cell in order to support the handover of the mobile stations, thereby notifying the mobile stations of neighbor base-station state information. That is, when a mobile station located in a cell moves into a neighbor cell, the mobile station can perform a handover because the mobile station already understands a neighbor cell's base-station information such as a network identifier and channel characteristics broadcast from the base station.
Table 1 below shows the format of a conventional MOB_NBR-ADV message used to report neighbor base station information from a base station to a mobile station. These message formats are generally known in the art, so a detailed description thereof will be omitted for the sake of clarity.
TABLE 1SyntaxSizeNotesMOB_NBR-ADV_Message_Format( ){Management Message Type = 53 8 bitsOperator ID24 bitsUnique ID assigned to the operatorConfiguration Charge Count 8 bitsIncremented each time theinformation for the associatedneighbor BS has changed.Fragmentation Index 4 bitsThis field indicates the currentfragmentation index.Total Fragmentation 4 bitsThis field indicates the total numberof fragmentationsSkip-Optional-Fields Flag 1 bitIf set to ‘1’ and if a neighbor hasOFDMA PHY the BS-ID for thatneighbor is omitted in this message.If set to ‘0’, BS-ID is not omitted forany neighbor.N_NEIGHBORS 8 bitsFor (j=0; j<N_NEIGHBORS; j++){Length 8 bitsLength of message informationwithin the iteration ofN_NEIGHBOR in bytes.PHY Profile ID 8 bitsAggregated IDs of Co-located FAIndicator, FA ConfigurationIndicator, FFT size, Bandwidth,Operation Mode of the startingsubchannelization of a frame, andChannel Numberif (FA Index Indicator = = 1) {FA Index 8 bitsThis field, Frequency AssignmentIndex, is present only the FA IndexIndicator in PHY Profile ID is set.Otherwise, the neighbor BS has thesame FA Index or the centerfrequency is indicated using the TLVencoded information.}if (BS EIRP Indicator = = 1) {BS EIRP 8 bitsSigned Integer from −128 to 127 inunits of dBm This field is presentonly if the BS EIRP indicator is setin PHY Profile ID. Otherwise, theBS has the same EIRP as the servingBS.}Neighbor BS-ID24 bitsThis is an optional field for OFDMAPHY and it is omitted or skipped ifSkip Optional Fields Flag = ‘1’Preamble Index 8 bitsThe index for the PHY profilespecific preamble. Preamble Index isPHY specific for SCa and OFDMA.The value of Preamble Index shall beignored and a value of ‘0x00’ shallbe used for OFDM PHYHO Process Optimization 8 bitsHO Process Optimization isprovided as part of this message isindicative only. HO processrequirements may change at time ofactual HO. For each bit location, avalue of ‘0’ indicates the associatedreentry management messages shallbe required, a value of ‘1’ indicatesthe reentry management messagemay be omitted. Regardless of theHO Process Optimization TLVsettings, the Target BS may sendunsolicited SBC-RSP and/or REG-RSP management messages Bit #0:Omit SBC-REQ/RSP managementmessages during current re-entryprocessing Bit #1: OmitPKM-REQ/RSP managementmessage during current re-entryprocessing Bit #2: OmitREG-REQ/RSP management duringcurrent re-entry processing Bit #3:Omit Network Address Acquisitionmanagement messages duringcurrent reentry processing Bit #4:Omit Time of Day Acquisitionmanagement messages duringcurrent reentry processing Bit #5:Omit TFTP management messagesduring current re-entry processingBit #6: Full service and operationalstate transfer or sharing betweenServing BS and Target BS (ARQ,timers, counters, MAC statemachines, etc...)Scheduling Service Supported 4 bitsBitmap to indicate if BS supports aparticular scheduling service. ‘1’indicates support, ‘0’ indicates notsupport: bit 0: Unsolicited GrantService (UGS) bit 1: Real-timePolling Service (rtPS) bit 2: Non-real-time Polling service (nrtPS)bit 3: Best Effort value of ‘1111’indicates no information on serviceavailable  Available Radio Resource 4 bitsPercentage of reported averageavailable subchannels and symbolsresources per frame 0000: 0% 0001:20% 0010: 40% 0011: 60% 0100:80% 0101: 100% 0110-1110:reserved 0110-1110: reserved valueof ‘1111’ indicates no information onservice available Hand Off Neighbor Preference 2 bits00 Normal 01 Preferred 10 Non-Preferred 11 ReservedDCD Configuration Change Count 4 bitsThis represents the Neighbor BScurrent DCD configuration changecountUCD Configuration Change Count 4 bitsThis represents the Neighbor BScurrent UCD configuration changecountTLV Encoded Neighbor informationVariableTLV specific   }   }
The following Table 2 illustrates information included in a TLV Encoded Neighbor information field of the MOB_NBR-ADV message, which includes a downlink channel descriptor setting (DCD_settings) field and an uplink channel descriptor setting (UCD_settings) field.
TABLE 2NameType (1 byte)Length (1 byte)Value (Variable-length)DCD_settingsVariableThe DCD_settings is a compound TLVvalue that encapsulates a DCD messagethat may be transmitted in the advertisedBS downlink channel. This information isintended to enable fast synchronization ofthe SS with the advertised BS downlink.The DCD settings fields shall contain onlyneighbor's DCD TLV values which aredifferent from the Serving BScorresponding values. For values that arenot included, the MSS shall assume theyare identical to the serving BSscorresponding values.UCD_settingsVariableThe UCD_settings is a compound TLVvalue that encapsulates a UCD messagethat may be transmitted in the advertisedBS downlink channel. This information isintended to enable fast synchronization ofthe SS with the advertised BS uplink. TheUCD settings fields shall contain onlyneighbor's UCD TLV values which aredifferent from the Serving BS'scorresponding values. For values that arenot included, the MSS shall assume theyare identical to the serving BS'scorresponding values.
The DCD_settings field in Table 2 is configured using the TLV value of a DCD message, which may be expressed in the format of Table 3. Such a DCD_settings field is generally known in the art, so a detailed description thereof will be omitted for the sake of clarity.
TABLE 3TypeName(1 byte)LengthValue (variable length)PHY scopeDownlink_Burst_Profile1May appear more than onceAll(see 6.3.2.3.1). The length isthe number of bytes in theoverall object, includingembedded TLV itemsBS EIRP22Signed in units of 1 dBM.AllFrame duration34The number of PSs containedSCin a Burst FDD or TDDframe. Required only forframed downlinksPHY Type41The PHY Type to be used.SCPower adjustment rule510 = Preserve Peak PowerSC, SCa1 = Preserve Mean PowerDescribes the poweradjustment rule whenperforming a transition fromone burst profile to another.Channel Nr61Downlink channel number asSCa,defined in 8.5. Used forOFDM,license-exempt operationOFDMAonly.TTG71TTG (in PSs)SCa,OFDM,OFDMARTG81RTG (in PSs)SCa,OFDM,OFDMARSSIR,max92Initial Ranging Max.AllReceived Signal Strength atBS Signed in units of 1 dBmChannel Switch Frame103Channel switch frameSCa,Numbernumber as defined in 6.3.15.7,OFDM,Used for license-exemptOFDMAoperation onlyFrequency124Downlink center frequencyAll(kHz).BS ID136Base Station IDSCa,OFDM,OFDMAFrame Duration Code141The duration of the frame.OFDMThe frame duration codevalues are specified in Table230.Frame Number153The number of the frameOFDMcontaining the DCD message.
The conventional base station periodically broadcasts a MOB_NBR-ADV message including a TLV encoded neighbor information field as shown in Table 1 in order to notify a mobile station of neighbor base station information. Meanwhile, information related to a base station identifier (BS_ID) field included in the DCD_settings is an iteration of information related to neighbor base-station identifier (neighbor BS_ID) of the MOB_NBR-ADV message. That is, the BS_ID information of the DCD_settings can be recognized by using a neighbor BS_ID and an operator identifier of the MOB_NBR-ADV message. Therefore, the conventional system repeatedly transmits the TLV information of the MOB_NBR-ADV message corresponding to the number of neighbor base stations, and incurs a signaling load due to iterative transmission of the BS_ID of the DCD_settings field.
In addition, an operator identifier (ID) included in the MOB_NBR-ADV message in order to report information about a network operator as shown in Table 1 does not change while a mobile station is using the same network operator. Therefore, when operator ID information is included in every transmitted MOB_NBR-ADV message, overhead may increase, degrading transmission efficiency.